It is well-known to form compressed air motors which include a housing forming a body, sealed by at least a cover sealingly mounted and in which at least two cylindrical gears with parallel axes rotate freely, one of which has a power take-off output shaft for co-operation or non co-operation with a speed reducing device incorporated within said body. A fluid inlet and outlet are provided on the lid or cover on either side of the common axis of said gears, while mobile inserted shoes of semi-circular shape disposed within the housing are provided with O-ring seals for application on the outside periphery of said gears to define the working chamber while preventing any fluid leakage that would be detrimental to the proper operation of the device.
This well-known embodiment of a pneumatic motor has important disadvantages, more particularly:
The faultless machining which is necessary for the curvilinear face of each shoe, which must correspond accurately to the outside diameter of the gear.
The necessary arrangement of an O-ring seal interposed between the gear and the shoe, and also between the ends of the curvilinear portions thereof and the portions of the housing adjacent thereto, in order to ensure a total sealing on the edges.
The necessity of a total sealing of the casing, inclusive of the accommodation of the shoes relative to the cover and to the other fastening means thereof.
The necessary use of a seal the ends of which are folded back against the adjacent sides of the housing with interposition of an elastic wedge.
The use of a flowing seal of plastic, such as tetrafluorethylene, which becomes easily scratched upon contact with the dirt contained in the air.
The necessity of a running in prior to putting the motor in operation.
The impossibility for the user to change the shoes.
The high cost price involved by reason of the machining operations and of the great number of parts.